Great willowherb is a perennial plant, reaching a height of ca. 80-180 cm. Its flowers are purple-pink with diameter of 15-25 mm. The leaves are long and thin, at widest below the middle, which makes them resemble the leaves of the willow, hence the name of the plant - in Bulgarian „vurbovka“ and in English - Great willowherb. They are covered more or less with tiny hairs, as the stems are covered with rare or dense, long hairs. The stems are cylindrical, sometimes with slightly ribbed base, standing erect or exhilarated; in height from 50 to 150-200 cm. The plant has thick, curved rhizomes.
The willowherb blooms from June to September. During flowering, the roots form long, fleshy wintering shoots, which serve as vegetative propagation. The plant can multiply also through seeds hidden in the fruit - box. The seeds are brown, reversed egg-shaped and covered with oblong warts.
The species is widespread at river sides in Bulgaria. It prefers moist sites and is important as a habitat of many aquatic creatures. Great willowherb originated from Eurasia. It is similar to other members of the genus Epilobium (Varbovka).